Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PTQ-0034 PATENT
METHODS AND COMPOSITIONS RELATING TO PHOSPHORYLATED MYOSIN
LIGHT CHAIN 1
Field of the Invention
The present invention relates to the identification of
two novel phosphorylation sites of myosin light chain 1
(MLC1). Phosphorylation of MLC1 at these sites was
demonstrated to increase in vivo following pharmacologic
preconditioning with adenosine. Monitoring MLC1
phosphorylation provides a useful means for identifying new
cardiac or skeletal muscle protective agents, monitoring the
extent of preconditioning of cardiac and skeletal muscle
tissue, and monitoring the status of a subject with cardiac
or skeletal muscle damage. Further, altering MLC1
phosphorylation serves as a means for changing contractility
of skeletal and cardiac muscle tissue and for protecting
skeletal and cardiac muscle tissue from damage caused by
conditions and/or factors including, but not limited to,
cardiomyopathies, hypertension, free radicals, ischemia,
hypoxia, and ischemia/hypoxia with reperfusion.
Background of the Invention
Ischemic preconditioning (PC), a phenomenon which exists
in all species examined, including humans(Cohen, M.V. and
Downey, J.M. Lancet 1993 342:6; Yellon et al. Lancet 1993
342:276-277; Kloner et al. J. Am. Coll. Cardiol. 1994
24:1133-1142), is a form of protection whereby a brief
ischemic episode reduces the extent of damage to cardiac
and/or skeletal muscle tissue from subsequent prolonged
ischemia (Murry et al. Circ. 1986 74:1124-1136). PC may also
be recruited pharmacologically, with one of many activators
being adenosine, a by-product of adenosine triphosphate (ATP)
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metabolism (Liu et al. Circ. 1991;84:350-356). Both ischemic
and pharmacological PC trigger two windows of protection, the
first (classical PC) becoming manifest within 15 minutes and
lasting 1-3 hours (Cohen, M.V. and Downey, J.M. Lancet 1993
342:6; Van Winkle et al. Cor. Art Dis. 1991 2:613-619; Li et
al. Am. Heart J. 1992 123:346-353; Lawson et al. J. Mol. Cell
Cardiol. 1993 25:1391-1402). The short duration of protection
afforded by classical PC is likely the result of post-
translational protein modifications, as 15 minutes does not
suffice to recruit de novo transcription and translation. In
contrast, the second window (late or delayed PC), which is
manifested 24-72 hours after the conditioning stimulus (Marber
et al. Circ. 1993 88:1264-1272; Kuzuya et al. Circ. Res. 1993
72:1293-1299) involves changes in gene expression (Bolli R.
Circ Res. 2000 87:972-983) as well as post-translational
protein modifications.
While the protective effect of PC is well established,
the molecular mechanisms of PC remain elusive. Current
research into classical PC focuses primarily on the opening
of the inner mitochondrial ATP-sensitive potassium (mitoKATP)
channel in response to activation of complex kinase signaling
cascades (Cohen et al. Annu. Rev. Physiol. 2000 62:79-109;
Marber, M.S. Circ. Res. 2000 86:926-931). Ischemia-induced
release of adenosine, bradykinin, opioids, and free radicals
leads to receptor-mediated activation of protein kinase C
(PKC) (Cohen et al. Annu. Rev. Physiol. 2000 62:79-109;
Marber, M.S. Circ Res. 2000 86:926-931). Kinases downstream
from PKC that have been implicated in PC include a tyrosine
kinase, and a number of mitogen-activated protein kinases
(MAPKs), the most likely candidates of which are in the c-Jun
N-terminal kinase (JNK) and p38 MAPK families (Cohen et al.
Annu. Rev. Physiol. 2000 62:79-109). A key downstream effect
of this cascade appears to be the opening of mitoKATP channels,
as pharmacological channel opening mimics genuine ischemic PC,
and mitoKATp channel blockers abolish cardioprotection (Grower,
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G.J. J. Cardiovasc. Pharmacol. 1994 24:518-S27). The
metabolic protective effects of channel opening may result
from a reduction in ATP hydrolysis (Garlid et al. Circ Res.
1997 81:1072-1082) and an influx of Caz+into the mitochondria
(Holmuhamedov et al. FASEB J. 1999 13:A1079(Abstr)). PC has
also been demonstrated to protect against functional
myofilament changes of stunned myocardium in rat trabeculae
(Perez et al. Cardiovasc. Res. 1999 42: 636-643) , thus implying
that modification to myofilament proteins may also potentiate
protection.
Summary of the Invention
An object of the present invention is to provide methods
for identifying agents which protect cardiac, skeletal and
smooth muscles from damage via their ability to increase MLC1
phosphorylation in the muscle tissue.
Another object of the present invention is to provide
methods and compositions for protecting cardiac and skeletal
muscles from damage by increasing phosphorylation of MLCl in
the muscle tissue.
Another object of the present invention is to provide
methods and compositions for altering the contractility of
cardiac and skeletal muscles by modulating MLC1
phosphorylation in the muscle tissue.
Another object of the present invention is to provide
methods for monitoring the phosphorylation status of MLCl in
a subject. Such methods are useful in evaluating whether or
not a subject is adequately protected from damage to cardiac
and skeletal muscles caused by conditions and/or factors such
as cardiomyopathies, hypertension, free radicals, ischemia,
hypoxia, and ischemia/hypoxia with reperfusion. In addition,
the status of MLCl phosphorylation is useful in assessing the
status of myocardial damage in a subject.
Yet another object of the present invention is to
provide methods for identifying kinases and/or phosphatases
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that act on MLC1 as therapeutic targets for agents that
modulate or protect against damage to cardiac and skeletal
muscles.
Brief Description of the Figures
Figure 1 provides a model of the structure of the Sl
portion of myosin including myosin light chain 1 (MLC1),
myosin light chain 2 (MLC2) and the myosin heavy chain
globular head and lever regions. The phosphorylation sites
are highlighted.
Figure 2 shows silver stained 2-DE gels of rabbit
ventricular myocyte proteins subjected to the "IN Sequence"
protein extractions described in Example 2. Figure 2A shows
a silver stained 2-DE gel of the whole cell homogenate within
a pH range of 3.0 to 10Ø Figure 2B shows a silver stained
2-DE gel of the first extract (proteins soluble at pH 7.4)
containing the cytosolic fraction within a pH range of 3.0 to
10Ø Figure 2C shows a silver stained 2-DE gel of the second
extract (protein soluble at pH 2.0) which is enriched for
myofilament protein within a pH range of 4.0 to 7Ø
Figure 3 shows examples of adenosine-induced
modifications to the rabbit ventricular myocyte proteome.
Whole cell homogenates of rabbit ventricular myocyte proteins
were separated by 2-DE to identify adenosine-induced protein
modifications. Shown is a representative silver-stained 2-DE
gel of adenosine-treated myocytes at a protein load of 250 ug
(pH 4-7). Positions of adenosine-induced protein
modifications observed are indicated by dashed boxes,
designated 1 (~40 kDa, pI ~4.8) and 2 (~26 kDa, pI ~4.6-5.0).
Enlargements of Regions 1 and 2 from 2-DE gels of adenosine-
treated (Ado) and control (Ctrl) myocytes are shown in the
side panels for comparison. The positions of SDS-PAGE
molecular weight standards are indicated on the left of the
2-DE gel.
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Figure 4 shows adenosine-induced changes to a rabbit
ventricular myocyte cytosolic subproteome. Cytosolic
subproteomes obtained by "IN Sequence" sequential extraction
at pH 7.4 were separated by 2-DE to identify adenosine-induced
protein modifications. The large panel (pH 3-10 linear
gradient) shows a silver-stained gel of adenosine-treated
cytosolic extract (90% of the protein extracted from 750 ug
of whole-cell homogenate). Adenosine-induced protein
modifications observed in these extracts are indicated by
dashed boxes, designated 3 (~28 kDa, pI ~5.5), 4 (~37 kDa, pI
~8.5), and 5 (~36 kDa, pI ~6.0). Enlargements of these
regions from 2-DE gels of adenosine-treated (Ado) and control
(Ctrl) samples are shown in the side panels for comparison.
The positions of SDS-PAGE molecular weight standards are
indicated on the left of the 2-DE gel.
Figure 5 shows adenosine-induced changes to a rabbit
ventricular myocyte myofilament-enriched subproteome.
Myofilament-enriched subproteomes obtained by "IN Sequence"
sequential extraction at pH 2.0 were separated by 2-DE to
identify adenosine-induced protein modifications. The large
panel (pH 4-7 linear gradient) shows a silver-stained gel of
adenosine-treated myofilament-enriched extract (containing l00
trifluoroacetic acid (TFA)-solubilized protein isolated from
cytosolic extract pellets from the extraction shown in Figure
4). An adenosine-induced protein modification observed in
these extracts is indicated by a dashed box, designated 2, as
it corresponds to Region 2 indicated in Figure 3 (~26 kDa, pI
~4.7-5.0). Enlargement of this region from 2-DE gels of
adenosine-treated (Ado) and control (Ctrl) samples is shown
in the side panel for comparison. The positions of SDS-PAGE
molecular weight standards are indicated on the left of the
2-DE gel.
Figure 6 shows MLC1 phosphorylation and adenosine
induced modulation in rabbit ventricular myocytes. Western
blots of 2-DE resolved rabbit ventricular myocyte whole-cell
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homogenates probed with an anti-ventricular MLC1 mAb (pH 4-7)
are shown in panel A. Prior to 2-DE, a single aliquot of
adenosine-treated myocytes was divided into two equal
portions, with one aliquot subjected to alkaline phosphatase
dephosphorylation (lower panel) for comparison to the
adenosine-treated myocytes (upper panel). Panel B shows the
position of MLCl (Region 2) from composite images of
myofilament-enriched extracts of adenosine-treated (upper
panel) and control myocytes (lower panel), illustrating the
difference in the amount of mono-phosphorylated MLC1.
Figure 7 shows mass spectrometry of MLC1.
Identification of MLC1 by tryptic peptide mass fingerprinting
was carried out as outlined in the methods section. A typical
MLCl spectrum of mass peaks obtained between 400 and 1500 Da
is shown in panel A. Two tryptic peptide fragments, with
masses of 790.845 (panel B, top) and 558.667 Da (panel C,
top), present in spectra obtained from unphosphorylated MLCl
spots were reduced markedly in spectra from monophosphorylated
MLCl spots. Instead, two additional fragments were detected,
with masses of 870.764 (panel B, bottom) and 638.601 Da (panel
C, bottom). The 80 Da shifts correspond to the addition of
a phosphate moiety. Peptide mass fingerprinting and sequence
alignments matched the altered fragments to theoretical
tryptic digests of rat and human ventricular MLC1. Sequence
analysis matched these phosphorylated peptide fragments with
rat and human fragments containing phosphorylatable residues,
corresponding to Thr69 and Ser200 for rat (Thr64 and Serl94
or 195 for human MLC1).
Figure 8 provides western blots of a MLCl 2-DE gel in
an in vivo swine model following acute injury (stunning) and
chronic injury (heart failure, HF) to the myocardium.
Detailed Description of the Invention
All cited patents, patent applications, and publications
are incorporated herein by reference in their entirety.
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Proteomics is a method of observing, concomitantly, changes
to the entire protein complement (proteome) of a particular
tissue or organ. Proteomic analyses are routinely carried out
by methods of protein separation, such as two-dimensional gel
electrophoresis (2-DE) or high performance liquid
chromatography (HPLC), followed by methods of protein
identification and characterization, including immunodetection
and mass spectrometry. 2-DE is a powerful technique for
resolving hundreds to thousands of proteins at one time, while
simultaneously enabling the resolution of a single protein
into its various post-translationally modified forms. This
facilitates identification of subtle protein changes, which
may be associated with a particular condition or disease
state. However, while 2-DE gels separate hundreds to
thousands of proteins, differences in charge, hydrophobicity,
and protein copy number (abundance) make it impractical to
inspect an entire proteome within a single gel.
A subproteomic approach, whereby proteins are analyzed
after fractionation by specific characteristics (i.e. charge,
solubility, intracellular location), facilitates investigation
of highly complex proteomes (Cordwell et al. Electrophoresis
2000 21:1094-1103).
In the present invention, an extraction method, referred
to herein as the "IN Sequence" extraction method was used to
reduce proteome complexity and isolate a single extract
enriching for many myofilament proteins. The myofilament
proteins are the most highly abundant proteins in muscle
cells, making "IN Sequence" particularly useful for proteomic
studies of muscle. Not only do the myofilament proteins
fractionate together, but the fact that they do facilitates
not only their investigation, but also that of numerous lower
abundance proteins. For example, loading may be increased in
myofilament-free extracts to study lower abundance proteins,
without interference by these highly abundant myofilament
proteins. Furthermore, reduction of proteome complexity
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enables detection and quantification of very subtle post-
translational protein modifications, such as that observed
with increased MLCl phosphorylation by adenosine-induced
preconditioning. Quantification of such changes would
otherwise be severely limited, if not impossible, due to the
contribution of other co-migrating proteins present in the
whole cell proteome.
Using proteomic analysis, protein modifications involved
in triggering classical pharmacological preconditioning (PC)
were investigated. A novel phosphorylation of ventricular
myosin light chain 1 (MLCl), also referred to as essential
light chain (ELC) and DTNB (5,5'-dithiobis-(2-nitrobenzoic
acid) light chain, the extent of which increased significantly
upon adenosine-induced PC, was identified. Insofar as LC1~,
the essential light chain (ELC) of smooth muscle, is expected
to have one or more phosphorylatable sites, the invention is
also applicable to smooth muscle.
In these experiments, proteins from isolated rabbit
ventricular myocytes were first resolved by two-dimensional
gel electrophoresis and then detected by silver staining. The
silver stained 2-DE gels of rabbit ventricular myocyte
proteins, resolved in a linear pH range of 3-10, revealed
roughly 1500 protein spots at greatly varying abundances. At
lower protein loads, adenosine-induced protein changes were
evident in silver-stained 2-DE gels of whole cell homogenates.
To facilitate protein modification analysis, sequential
subproteomes were isolated using the "IN Sequence" extraction
protocol as described in Example 2. Numerous low abundance
proteins were enriched following the initial extractions at
physiological pH, enabling visualization of protein changes
not evident in whole cell homogenates. Approximately 800
protein spots were detected in these extracts. Subsequent
acid extraction greatly enriched many of the high abundance
myofilament proteins. As the pI of most of these proteins is
close to pH 5, their resolution was improved by separation
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with a narrower pH gradient of 4-7, yielding 55 detectable
protein spots (see Figure 2).
Using the BioImage software INVESTIGATORT" HT Proteome
Analyzer 1Ø1 (Genomic Solutions, Inc.), composite images of
protein spots were prepared from individual silver-stained 2
DE gels for four sets of paired adenosine-treated and
untreated cardiomyocytes obtained from different rabbit
hearts. All spots were quantified and matched, then
normalized by a match ratio method using 2-DE gels at optimal
staining levels. Accurate quantification of protein spots was
possible only when it was determined that the spot intensity
was within a linear range of concentration for silver
staining, and therefore neither saturated nor under
represented.
Comparison of adenosine and control composite images
revealed that myofilament-enriched acid extracts possessed a
highly reproducible difference for a series of three spots
with a relative migration (Mr) of ~26 kiloDaltons (kDa) and an
isoelectric point (pI) range of ~4.7-5.0 (See Figures 3 to 5).
Based on relative protein abundance, pI, Mr, and comparison to
known ventricular protein 2-DE gel databases, these spots were
suspected to be myosin light chain 1 (MLCl). This was
confirmed by western blotting of 2-DE separated whole cell
homogenates with an antibody specific for MLC1, which showed
a three spot alignment identical to those observed for both
the composite image and the silver stained gels (see Figure
6). Dephosphorylation of protein from adenosine-treated
myocytes prior to 2-DE separation revealed that MLC1 was
phosphorylated, as the three spot pattern collapsed to a
single spot, corresponding to the most basic of the three
original protein spots. Thus, MLCl was present in rabbit
ventricular myocytes as a mixed population of un-, mono-, and
di-phosphorylated protein. To ensure that MLC1 modification
was not an artifact occurring during the experimental
protocols, the "IN Sequence" extraction and 2-DE separation
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of proteins extracted directly from intact rabbit ventricular
tissue were repeated and the same three spot pattern for MLCl
was observed by both silver staining and immunoblotting.
The percentages of the various MLCl forms were quantified
from the silver stained 2-DE gels under optimal staining
conditions for MLC1 in all gels, such that all three MLC1
spots were neither under nor over represented. MLCl
phosphorylation increased from 25.7 ~ 1.60 (mean ~ standard
error) in drug-free controls, to 34.0 ~ 2.7o following
treatment with adenosine. This change in MLC1 phosphorylation
was found to be statistically significant (P<0.05) by one way
ANOVA.
Mass spectrometry was then performed on protein isolated
from silver stained 2-DE gels (see Figure 7). Analysis of
trypsin-digested protein fragments isolated from each of the
three spots resulted in highly consistent mass spectra. Two
variations were identified between spectra obtained from
unphosphorylated and phosphorylated MLCl spots, indicating
differences in the peptide fragments present. Fragments with
masses of 558.667 and 790.845 Da were present in
unphosphorylated MLC1 spectra, but were conspicuously absent
from phosphorylated samples. Instead, the spectra obtained
from the phosphorylated MLC1 samples contained two other
fragments that were not present in unphosphorylated samples,
with masses of 638.601 and 870.764 Da. Addition of a
phosphate moiety (79.9797 Da) to each of the two unique
fragments in the upper spectra resulted in phosphopeptides
varying in mass by less than 0.1 Da from the two unique
fragments in the lower spectra.
Peptide mass fingerprinting matched theoretical tryptic
peptide fragments derived from rat ventricular MLCl sequence
(GenBank Accession No. P16409) to both the 638.601 and 870.764
Da phosphopeptides of rabbit MLC1. Rat MLCl amino acids
(a. a.) 196-200 matched the smaller phosphopeptide fragment,
while a.a. 69-75 matched the larger phosphopeptide fragment.
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Using Clustal W (version 1.81), these peptides were found to
align with human ventricular MLC1 (GenBank Accession No.
P08590) a.a. peptide fragments 64-70 and 191-195,
respectively. Each of the identified fragments contains a
potential phosphorylation site, at Thr69 and Ser200 for rat
MLC1, and at Thr64 and Serl94 or Serl95 for human MLCl.
Clustal W sequence alignments also revealed that these two
regions of MLC1 were highly conserved among species and across
muscle types. The same pattern of phosphorylation of MLCl has
been observed not only in humans, but also in rats, dogs and
swine.
As discussed above and in the below examples,
phosphorylation of MLC1 after a 60 minute exposure of cells
to adenosine was about 340. However, adenosine exposure
results in a rapid second messenger response. Therefore, a
larger increase in MLCl phosphorylation is expected to occur
within the first 60 minutes period of adenosine exposure
(e. g., within the first 5 to 10 minutes), with a subsequent
decline to the steady-state value in a normal healthy subject
of about 25o thereafter. The 34% phosphorylation discussed
herein is likely a value along the decline to steady-state.
This can be confirmed by monitoring the extent of MLC1
phosphorylation over a 60 minute period to produce a time
course of phosphorylation. The provision of a such time
course will enhance therapeutic and diagnostic aspects of the
invention, as, for example, it will allow the extent of damage
to be more accurately assessed.
The present invention provides the first demonstration
of in vivo MLCl phosphorylation via the identification of
these two novel phosphorylation sites. Based on the highly
conserved sequence of MLCl and the crystal structure of the
myosin head region (Rayment et al. Science 1993 261:50-8), it
is believed that both phosphorylation sites reside in exposed
regions of the protein near the myosin heavy chain (MHC) lever
arm. The serine site is located directly adj acent to the MHC
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lever arm extending through MLCl, while the threonine site is
located in the region of closest proximity between MLC1 and
MLC2, a protein which is also associated with the MHC lever
arm adjacent to MLCl (see Figure 1). The fact that the level
of phosphorylation increased significantly upon adenosine-
induced PC is indicative of MLCl phosphorylation serving as
a protective end effector of adenosine preconditioning.
Accordingly, one aspect of the present invention relates
to methods for identifying agents protective against cardiac
and skeletal muscle damage by the ability of the agent to
increase MLCl phosphorylation. Agents identified as
increasing MLC1 phosphorlyation inhibit damage to cardiac and
skeletal muscles caused by conditions and/or factors
including, but not limited to, cardiomyopathies, hypertension,
free radicals, ischemia, hypoxia, and ischemia/hypoxia with
reperfusion. These agents are also referred to herein as
muscle protective agents. Such agents are useful in
protecting muscle in, for example, surgical procedures, heart
transplant, and heart harvesting.
The ability of a potential muscle protective agent to
increase MLCl phosphorylation can be assessed in vitro in
purified cardiac or skeletal myosin, myosin light chain l, or
isoforms thereof, or in myofilament or skinned muscle fibers.
In one embodiment, adenosine triphosphate (ATP) and the
potential protective agent are added to the purified myosin,
myosin light chain 1 or isoform thereof, or the myofilament
or skinned muscle fiber and the phosphorylation of MLC1 is
monitored. MLCl phosphorylation can be detected by various
methods including, but not limited to, 2-DE using either a
general or specific anti-MLCl antibody, silver staining or 32P
labeling, and 1-DE using either 32P or anti-phospho-specific
antibody. For example, monitoring after heart surgery or
transplant provides information about the status of a
patient's recovery.
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The ability of a potential muscle protective agent to
increase MLCl phosphorylation can also be assessed in isolated
myocytes or whole hearts either isolated using Langendorff
apparatus or in vivo. In these embodiments, the ability of
a potential muscle protective agent to trigger preconditioning
can be assessed by monitoring MLC1 phosphorylation status.
MLCl phosphorylation in these embodiments can also be detected
by methods such as 2-DE using either an anti-MLCl antibody,
silver staining or 32P labeling, or 1-DE using either 32P or
anti-phospho-specific antibody.
The ability of a potential muscle protective agent to
increase MLCl phosphorylation can then be confirmed in vivo
by administering the agent to a subj ect and monitoring the
level of MLCl phosphorylation in a biological sample of the
subject. For purposes of the present invention, by
"biological sample" it is meant to include, but is not limited
to, biological fluids such as serum, plasma, urine, milk,
lymph, amniotic fluid, semen and cerebrospinal fluid, and
biological tissues, such as cardiac, skeletal, and smooth
muscle. In a preferred embodiment, the biological sample is
serum.
In all of these embodiments, it is preferred that MLC1
phosphorylation levels be determined in the presence and
absence of the potential muscle protective agent. An increase
in the MLC1 phosphorylation levels in the presence of the
agent as compared to the MLCl phosphorylation levels in the
absence of the agent is indicative of the agent being
protective of the myocardium against damage caused by
conditions and/or factors including, but not limited to,
cardiomyopathies, hypertension, free radicals, ischemia,
hypoxia, and ischemia/hypoxia with reperfusion.
Agents identified as protective may be administered as
pharmaceutical compositions to a subject in need of a muscle
protective agent. Methods for formulating these agents with
a biocompatible carrier to produce a pharmaceutical
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composition are well known and taught in standard reference
text books such as Pharmaceutical Dosage Forms (Lieberman,
Rieger and Banker (Eds.), 1988, Marcel Dekker, Inc., New York,
N.Y.) and Remington~s Pharmaceutical Sciences, Mack Publishing
Co. , Easton, PA, 1985. Thus. toharmar~~",t-;.~~~ ~.-",......, _~_ ___
comprising muscle protective agents identified in accordance
with the teachings provided herein and a biocompatible carrier
can be prepared routinely by those of skill in the art . These
agents can also be incorporated into cardioplegia solutions
(e. g, cardioplegia solution Catalog No. 2B1462 from Baxter
Healthcare Corp.) used during heart surgery and to transport
donor hearts for transplantation. It is preferred that the
muscle protective agent of the compositions and cardioplegia
solutions not be adenosine.
Accordingly, the present invention also relates to
methods and compositions for protecting the cardiac and
skeletal muscle from damage by increasing phosphorylation of
MLC1 in the muscle. Compositions comprising an agent which
increases phosphorylation of MLC1 and a biocompatible carrier
can be administered to a subject in need thereof to protect
muscle from damage resulting from or caused by conditions
and/or agents including, but not limited to, cardiomyopathies,
hypertension, free radicals ischemia, hypoxia, and
ischemia/hypoxia with reperfusion. For example, in one
embodiment an agent identified as increasing MLC1
phosphorylation can be administered to a subject prior to a
surgical procedure wherein it is suspected that cardiac or
skeletal muscles will be exposed to ischemic and/or hypoxic
conditions. Examples of such procedures include, but are not
limited to, coronary artery bypass surgery, heart transplants,
angioplasty, and valve replacements. Agents identified as
increasing MLC1 phosphorylation can also be administered to
subj ects exhibiting chest pain as a means of decreasing inj ury
to the heart resulting from a potential infarction. Such
agents can also be administered to a subject prior to
administration of a chemotherapeutic agent such as radiation
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therapy known or suspected to cause damage to the skeletal
and/or cardiac muscles.
Administration of agents which modulate MLC1
phosphorylation also alter contractility of cardiac and
skeletal muscles. Accordingly, the present invention also
relates to methods and compositions for altering contractility
of cardiac and skeletal muscles by contacting the muscle with
an agent which modulates MLC1 phosphorylation status. By the
term "modulate", "modulating", or "modulation" as used herein,
it is meant either an increase in MLC1 phosphorylation or a
decrease in MLCl phosphorylation. Such methods and
compositions are useful in increasing muscle function
following a surgical procedure wherein the muscle was stunned
or in conditions such as heart failure wherein the muscle is
weakened and cannot maintain its required output.
The present invention also relates to methods of
monitoring the phosphorylation status of MLC1 in a subject to
evaluate whether or not cardiac and skeletal muscles are
protected from damage resulting from conditions and/or factors
including, but not limited to, cardiomyopathies, hypertension,
free radicals, ischemia, hypoxia, and ischemia/hypoxia with
reperfusion. This method is useful in assessing the level of
protection of cardiac and skeletal muscles in a subject prior
to and following a surgical procedure, particularly heart
surgery, as well prior to administration of a chemotherapeutic
agent such as radiation therapy which may result in damage to
the muscle tissue.
In addition, monitoring the phosphorylation status of
MLCl provides a means for assessing the status of cardiac
and/or skeletal muscle damage in a subject. For example, MLC1
has been shown to be phosphorylated in acute injuries of the
myocardium such as preconditioning and early stages of
ischemic injury (see Figure 8). However, phosphorylated MLC1
was not observed in the myocardium in chronic conditions such
as heart failure (see Figure 8). In fact, levels of
phosphorylated MLC1 in this heart failure model were equal to
or less than basal levels measured in control animals.
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Accordingly, the phosphorylation status of MLC1 is believed
to be useful in distinguishing early damage to the myocardium
from more severe, longer term damage. Further, it is believed
that administration of a muscle protective agent which
increases MLC1 phosphorylation can be used to raise levels of
MLC1 phosphorylation in subjects suffering from chronic heart
failure, thereby alleviating further damage to the heart and
increasing heart function.
The identification of MLC1 phosphorylation sites also
facilitates identification of kinases and/or phosphatases that
act on MLC1, and in particular MLC1 phosphorylation. The
identification of such kinases and/or phosphatases will be
useful in identifying new therapeutic targets for agents which
modulate MLC1 phosphorylation status.
The following nonlimiting examples are provided to
further illustrate the present invention.
Examples
Example 1: Isolation and Preconditioning of Rabbit
Ventricular Myocytes
Rabbits were used in compliance with the Animals for
Research Act (Province of Ontario), the Canadian Council on
Animal Care, and the Guide for the Care and Use of Laboratory
Animals published by the US National Institutes of Health (NIH
publication No. 85-23, revised 1985).
Rabbit ventricular myocytes were isolated by collagenase
dissociation in accordance with procedures described by Liu
et al. (Circ. Res. 1996 78:443-454). In this procedure,
hearts were excised from anesthetized (30 mg/kg pentobarbital
IV) New Zealand White rabbits (weighing 1 to 2 kg) and mounted
on a Langendorff apparatus. The heart was subjected to
retrograde perfusion with modified Krebs-Henseleit solution
composed of (in mmol/L) NaCl 119, KC1 5, NaHC03 25, KH2P09 1,
MgSOq l , CaCl2 2 , and glucose 10 , with 95 % Oz / 5 % CO2 at 3 7
° C .
Hearts were equilibrated for five minutes, perfused without
Caz+ for five minutes, then with perfusate containing
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collagenase (1.0 mg/mL, Worthington type II) for fourteen
minutes. The perfusion pressure was monitored, and the flow
rate was adjusted to maintain perfusion pressure at ~75 mm Hg.
Ventricles were minced and cells were filtered through nylon
mesh and washed several times with a high-K+ solution
consisting of (in mmol/L) potassium glutamate 120, KCl 25,
MgCl2 1, N-2-hydroxyethyl piperazine-N-2-ethanesulfonic acid
(HEPES) 10, EGTA 0.1, and glucose 10. Cells were then washed
in a modified Tyrode's solution containing (in mmol/L) NaCl
140, KC1 5, CaCl2 1, MgCl2 1, and HEPES 10 (pH 7.4), yielding
>500 of Ca2+-tolerant ventricular myocytes.
Cell isolation was followed directly by pharmacological
preconditioning, which was carried out by treatment with 100
~amol/L adenosine (Sigma) for 60 minutes in a 37°C water bath
in accordance with the procedure described by Sato et al.
(Circ. 2000 102:800-805). Untreated cells were prepared
concurrently as controls. Equivalent 25 ~L aliquots of cells
(containing ~30 mg/mL of protein as determined by Lowry assay
(Lowry et al. J. Biol. Chem. 1951 193:265-275)) were frozen
in a dry ice/ethanol bath, and stored at -80°C until analysis.
Example 2: "IN Sequence" Protein Extraction and Protein
Dephosphorylation
Every step in the "IN Sequence" protein extraction
protocol was carried out on ice or at 4°C, and all
centrifugations were conducted at 4°C for 2 minutes at
16000xg. Aliquots (25 ~L) of myocytes were mechanically
homogenized in 100 uL of HEPES extraction buffer, consisting
of (in mmol/L) HEPES 25 (pH 7.4) , NaF 50, Na3V0q 0.25,
phenylmethylsulfonyl fluoride 0.25, EDTA 0.5, and (in umol/L)
leupeptin 1.25, pepstatin A 1.25. The homogenate was
centrifuged, and the supernatant removed and saved. A second
HEPES extraction was performed on the pellet and pooled with
the supernatant from the first extraction. The remaining
pellet was subjected to further extraction by mechanical
homogenization in 50 uL of acid extraction buffer, consisting
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of 1% v/v trifluoroacetic acid (TFA) and 1 mmol/L Tris (2-
carboxyethylphosphine) hydrochloride (pH ~2.0). Again, the
homogenate was centrifuged, and the supernatant removed and
saved. An additional TFA extraction was performed on the
pellet and pooled with supernatant from the previous TFA
extraction. The supernatants and remaining pellet were then
frozen and stored at -80°C. HEPES extractions (extracts 1 and
2) enrich for soluble cytosolic proteins, while TFA
extractions (extracts 3 and 4) enrich for many myofilament
proteins.
Proteins were dephosphorylated using the following
protocol. Essentially, 25 uL aliquots of myocytes were
mechanically homogenized to lyse cells, then divided into two
equal volumes 0375 ug protein each). A total of 2.5 ~aL of
lOX alkaline phosphatase reaction buffer was added to each
sample, consisting of (in mmol/L) NaCl 1000, MgCl2 100,
dithiothreitol (DTT) 10, Tris-HC1 500 (pH 7.9 at 25°C). To
one sample, a 10 uL aliquot of calf intestinal alkaline
phosphatase (10 units/~L, New England Biolabs) in 50% glycerol
and (in mmol/L) KC1 50, MgCl2 1, ZnClz 0.1, Tris-HC1 10 (pH
8.2) was added, while 10 uL of the same solution lacking
alkaline phosphatase was added to the control. Samples were
incubated at 37°C for 15 minutes and the reaction stopped by
addition of 20 volumes (500 ~L) of isoelectric focusing (IEF)
buffer (8 mol/L urea, 2 % w/v 3- [3-cholamidopropyl] -1-propane-
sulfonate, 0.5% pH 4.0-6.5 ampholytes, 50 mM DTT, and 0.01%
w/v bromophenol blue).
Example 3: Isoelectric Focusing (IEF)
IEF was carried out using a PROTEAN° IEF cell (Bio-Rad)
essentially according to the manufacturer s protocol. Protein
samples were initially dissolved in 500 ~L of IEF buffer,
loaded into the focusing tray, overlaid with 170 mm pH 4-7
immobilized linear pH gradient READY STRIPST" (Bio-Rad), then
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covered with mineral oil. Gels were actively rehydrated at
50 volts (V) for 10 hours to enhance protein uptake, then
subjected to the following conditions using a rapid voltage
ramping method limited by a maximum current of 50 uA per gel:
100 V for 25 Volt-hours (Vh) , 500 V for 125 Vh, 1000 V for 250
Vh, and 8000 V for 85 kVh. A Pettier temperature control
platform maintained gels at 20°C throughout IEF. Focused gels
were stored at -20°C prior to sodium dodecyl sulfate-
polyacrylamide gel electrophoresis (SDS-PAGE).
Example 4: Sodium Dodecyl Sulfate-Polyacrylamide Gel
Electrophoresis
IEF strips were thawed and equilibrated in two steps
prior to SDS-PAGE. First, strips were incubated for 10
minutes in equilibration buffer (50 mmol/L Tris-HC1, pH 8.8,
6 mol/L urea, 30% v/v glycerol, 2% w/v SDS) supplemented with
10 mg/mL DTT, followed by a 10 minute incubation in
equilibration buffer supplemented with 25 mg/mL iodoacetamide.
Then strips were rinsed once with SDS-PAGE buffer (25 mmol/L
Tris, 192 mmol/L glycine, pH 8.3, 0.1% w/v SDS) . Proteins
were then resolved by 12.5% SDS-PAGE with IEF strips embedded
in 5% stacking gel using a PROTEAN° II XL system (Bio-Rad, gel
dimensions of 192 x 184 x 1 mm). Electrophoresis was carried
out at 50 V for 30 minutes, followed by 150 V for 7.5 hours.
Example 5: Protein Transfer and Western Blotting
Following SDS-PAGE, gels were equilibrated in SDS-PAGE
buffer supplemented to 20% v/v methanol for 10 minutes, then
transferred to nitrocellulose (0.22 um pore size, Osmonics
Inc. ) at 200 mA constant current for a period of 2 hours using
a PROTEAN° TRAMS-BLOT° Cell (Bio-Rad). After transfer,
nitrocellulose membranes were rinsed with phosphate-buffered
saline/Tween-20 (PBS/T), consisting of (in mmol/L) NaCl 137,
KCl 2.7, Na2HP09 10.1, KHZPOq 1.8, pH 7.4 supplemented to 0.1%
v/v Tween-20, then blocked overnight at 4°C with 1% v/v
blocking reagent (Roche Diagnostics) in PBS/T. Western
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blotting for MLC1 was carried out using a monoclonal antibody
(mAb 39-121, provided by Spectral Diagnostics, Toronto, ON,
Canada) at 1 ug/mL, and detected using alkaline-phosphatase
conjugated anti-mouse IgG (Jackson ImmunoResearch
Laboratories) and Renaissance CDP-STAR° western blot
chemiluminescence reagent (NEN/Mandel) according to the
manufacturer's protocol.
Example 6: Silver Staining of 2-DE Gels
2-DE gels were silver stained according to the protocol
of Shevchenko et al. (Anal. Chem. 1996 68:850-858) which is
a reversible staining method compatible with subsequent
analysis of protein by mass spectrometry. In the procedure,
gels were incubated overnight in 50% v/v methanol, 5% v/v
acetic acid, followed by 50% v/v methanol for 10 minutes, then
10 minutes in deionized distilled (dd) HzO. Gels were
sensitized for 1 minute in 0.02% w/v sodium thiosulfate,
followed by two 1-minute ddH20 washes, then incubated in
prechilled (4°C) 0.1% w/v silver nitrate for 20 minutes,
followed again by two 1-minute ddHzO washes. Proteins were
then visualized by several washes with developing solution (2 %
w/v sodium carbonate, 0.04% v/v formalin) until a desired
level of staining was achieved, after which development was
stopped with 5% v/v acetic acid.
Example 7: Image Analysis and Quantification
Silver-stained 2-DE gels were digitized at 150 dpi
(pixels per inch) resolution using a POWERLOOKII° scanner
(UMAX° Data Systems, Inc.) on a SUN° ULTRA5TM computer (Sun
Microsystems, Inc.). Protein spots were then located,
quantified, and matched to spots on other gels with the
BioImage software INVESTIGATORTM HT Proteome Analyzer 1Ø1
(Genomic Solutions, Inc.). Fifteen manually defined spots
were selected as anchors for triangulation of remaining spots.
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Composite images were then prepared by matching spots from
four gel images for each treatment group (adenosine and
control), and normalized using a match ratio method to
compensate for differences in protein loading and level of
silver stain development between gels. Optimization of silver
staining was required, as protein quantity and extent of
staining time affects detection and quantification of
proteins. Gels used for quantification were all within the
optimal staining range for MLC1. Integrated intensities of
the three MLC1 spots were summed to give an overall integrated
intensity of MLC1 for each gel, then values were converted to
percentages of the total MLC1 for each of the three spots .
Thus, determination of the extent of phosphorylation (mean ~
standard error) was conducted within a single gel, and never
between gels, in order to minimize differences that invariably
arise when attempting to compare intensities between two
silver-stained images. One way ANOVA was used to determine
if a significant difference existed between experimental
groups.
Example 8: Mass Spectrometry
Protein spots extracted from 2-DE gels were destained
according to Gharahdaghi et al. (Electrophoresis 1999 20:601-
605), then dried under vacuum before enzymatic digestion with
sequence-grade modified trypsin (Promega). Tryptic peptides
were extracted with 50% acetonitrile (ACN) /5% TFA, dried under
vacuum, and reconstituted with 3 uL of 50% ACN/0.1% TFA.
Reconstituted extract (0.5 ;.zL) was then mixed with 0.5 uL of
matrix (10 mg/mL a-cyano-4-hydroxy-trans-cinnamic acid in 50%
ACN, 0.1% TFA), spotted on a stainless steel 100-well mass
spectrometry plate, and air dried. Samples were analyzed
using a VOYAGER° DE-Pro matrix-assisted laser
desorption/ionization time-of-flight (MALDI-TOF) mass
spectrometer (PerSeptive Biosystems) operated in the delayed
extraction/ reflector mode with an accelerating voltage of 20
kV, grid voltage of 72%, and a 50 nanosecond delay. Five
spectra (50-100 laser shots/spectrum) were obtained for each
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sample. External calibration was performed using a Sequazyme
Peptide Mass Standard kit (PerSeptive Biosystems) by spotting
the following standards adj acent to the sample on the mass
spectrometry plate: des-Arg-bradykinin, angiotensin-1, and
Glu-fibrinopeptide B.
Example 9: Bioinformatic Data Analysis
Peptide mass fingerprinting was conducted with the
database search tool MS-Fit in the program Protein Prospector
(version 3.2.1), available at http://prospector.ucsf.edu/.
A number of restrictions were applied to the initial search:
species - mammals, pI range = 4-7, mass range - 0-30 kDa (1
Da mass tolerance), with a minimum of 4 peptides to match, and
a maximum of one missed tryptic cleavage. Top candidate
proteins identified by MS-Fit were then analyzed for
theoretical tryptic peptide fragments using MS-Digest, taking
into account phosphorylation of Ser, Thr, and Tyr residues,
then compared to the observed spectra, allowing a mass
tolerance of 0.2 Da. MLC1 sequence alignments were prepared
with the program Clustal W (version 1.81) provided online by
the European Bioinformatics Institute at
http://www2.ebi.ac.uk/clustalw/.
Example 10: MLC1 Phosphorylation in Acute versus Chronic
Myocardial Damage
Model A: Ischemia induced failing heart model in swine
(complete occlusion and chronic (analyzed 6 weeks after
surgery))
Neutered male swine (13-34.0 kg) underwent open chest
surgery for occlusion of the mid-third of the left anterior
descending branch of coronary artery (LAD) to induce heart
failure. Sham-operated swine (SHAM) or controls underwent the
same surgical procedure except the LAD was not occluded.
During open chest surgery and at termination, animals were
under general anesthesia (a preanaesthetic, atropine followed
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by a combination of ketamine, midazolam and isoflurane, with
anesthesia maintained by isoflurane). Upon recovery the
animals received analgesics as needed. At 4 weeks,
echocardiography was performed on conscious mildly sedated
animals. To estimate the left ventricle ejection fraction
echocardiographs were performed in the lateral position, left
side of the swine down, using a PieMedical 200 scanner
equipped with a 5.0/7.5 MHz probe. At 6 weeks post-surgery
animals were sacrificed, the hearts were excised, immediately
snap-frozen in liquid nitrogen and stored at -80°C. All
experimental procedures conformed to guidelines of the
Canadian Council of Animal care and were approved by Queen's
University Animal Care Committee.
Model B - Ischemic induced stunning in swine (low flow done
on conscious animals acute for 60 minutes with about 40o blood
flow)
A left thoracotomy was performed in domestic swine
(weight, 22-25 kg), and the pigs were instrumented to measure
global and regional myocardial function in accordance with
procedures described by Kudej et al. (Circ. Res. 1998 82:1199-
2050 and Shen et al. (Circ. Res. 1995 76:479-88) . After 1
week of post-operative recovery, myocardial stunning was
induced by introducing air into the hydraulic occluder to
reduce coronary blood flow by approximately 40% for 90 minutes
and followed by 60 minutes full reperfusion. Stunned tissue
was taken from a region within ischemic zone. Control tissue
was taken from a region remote from the ischemic zone in same
animal.
SDS PAGE and 2-DE
Heart tissue from a non-infarcted region of the left
ventricle was homogenized in 20 mM Tris (pH 6.8) and 0.2 mM
sodium vanidate, 50 mM sodium fluoride, 2 mM EDTA, 1 ~M
leupeptin, 1 ~M pepstatin A, 0.36 ~aM aprotinin, 0.25 mM
phenylmethylsulfonyl fluoride at 4°C at a ratio of tissue
weight: buffer volume equal to 1:4 (whole tissue homogenate).
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2-DE was carried out as described herein. 100 ug of either the
cytoplasmic or myofilament protein enriched extracts, obtained
using the IN SEQUENCE extraction method described in Example
2, were diluted in 500 u1 of 8 M urea, 2.5 M thiourea, 4%
CHAPS (w/v), 0.5% pH 3.5-10 ampholyte (v/v) (Sigma, St. Louis,
MO, USA), 0.01% bromophenol blue (w/v). Samples were loaded
on a pH 3-10 immobilized linear gradient IPG Strips (170 mm)
and isoelectric focusing performed using a Protean IEF cell
system (Bio-Rad, Hercules, CA, USA). Gels were actively
rehydrated at 50 V for 10 hours, then rapid voltage ramping,
limited by maximum current of 50 ~zA per gel, was applied in
steps at 100 V (25 Vh) , 500 V (125 Vh) , 1000 V (250 Vh) and
8000 V to accumulate 65 kVh. In the second dimension proteins
from the strips were resolved on 12% SDS PAGE gels using a
Protean II XL system (Bio-Rad, Hercules, CA, USA)(192 mm x 184
mm x 1 mm) . For regular SDS PAGE (12.5%) a mini-Protean II
system (Bio-Rad, Hercules, CA, USA)(75 mm x 100 mm) was used.
Gels were either silver or Coomassie Blue stained. When
required, gels were transferred to nitrocellulose (NitroPure
nitrocellulose from Osmonics Inc., Westborough, MA, USA) and
western blot analysis was carried out. Primary antibody was
anti-myosin light chain 1, at 1 ~g/ml; secondary antibody was
alkaline-phosphatase conjugated anti-mouse IgG (ImmunoResearch
Laboratory, West Grove, PA, USA), at 1/10,000 dilution (stock
concentration 0.3 mg/ml); detection by Immun-Star
chemiluminescence system (BioRad, Hercules, CA, USA).
